Assume you are allowed to draw a credit of 1000 Euros of which you alreadygot 200 Euros from your bank last month. In other words, you can still obtain 800 Euros in the current month. If you today get another credit of 500 Euros, the CCF is 500 Euros divided by 800 Euros, which evaluates to 62.5%.
Critiques
A possible drawback of the CCF is that it is backward looking which might be not appropriate for evaluating the EAD at a given time.